Looking like a faraway moon, Venus shines in Earth's sky yesterday at dusk. Photo: Bob King

Venus made an otherworldly appearance between cloud layers last night 15 minutes after sunset, but hazy skies and low altitude made it impossible to see its little companion Mercury. Tonight might be the last night you’ll see Venus in the evening before Tuesday’s transit.

Look for it 2-3 degrees above the northwestern horizon right after sunset. Once found in binoculars, try to spot it with your naked eye.

Venus at 10 a.m. today photographed through a 4-inch scope. The cusps of the crescent extend a little around the shadowed side of the planet. Because of turbulence, Venus looks much thicker than a live view. Photo: Bob King

Today Venus is only five degrees east of the sun, with its nightside turned earthward. Only a super-slender crescent remains. When Venus is in its “full moon” phase, 100% of the planet is illuminated by the sun; today it’s down to 0.4%.

You’d think with so little surface area in sunlight, the planet would be much fainter than its -3.8 magnitude, but as the crescent narrows, its size increases as Venus approaches the Earth. That helps to compensate in good part for the shrinkage in area.

The planet has gradually faded from its maximum brightness of -4.6 magnitude reached on April 30. Before it passes in front of the sun and becomes a magnitude-less black dot, Venus will fade a tiny bit more to -3.7. To measure the brightness of an object in space, astronomers assign it a magnitude, a counterintuitive scale where the larger the number, the fainter the object. The brightest celestial objects have negative number magnitudes. Topping the list is the sun at -27!

Don Pettit created this amazing image by combining 18 long-exposure images taken with a camera mounted inside the International Space Station (ISS) on March 16, 2012. Cities show as streaks of orange below the station and the bright blotches are lightning. Since the ISS circles Earth once every 90 minutes, long exposures record stars as circular arcs centered on the station's north and south "poles". Credit: NASA/Don Pettit

NASA astronaut and flight engineer Don Pettit, famous for his many stunning photos taken from the International Space Station (ISS), plans to be the first person to observe and photograph a Venus transit from outer space. He’ll be using a Nikon D2Xs camera and an 800mm telephoto lens equipped with a white light solar filter. Pettit will got the approval from NASA to remove the non-optical quality, internal window panes called “scratch panes” from the space station’s cupola so he can get sharp images. If I could only do that in an airplane.

Another set of time exposures taken through one of the space station's cupola windows. Click photo for more a larger version and more details on how he made the pictures. Credit: NASA / Don Pettit

Petitt plans to post the photos during the transit. Since he’s a big Twitter guy, you check him out at astro_pettit. It should be interesting to see if Don will see the black drop effect without any atmosphere in the way.

On a final note, I inadvertently used the wrong set of NASA transit times in this earlier blog(now corrected). Though only several minutes off, they were incorrect.

Click HEREfor a table listing transit start, maximum and end times for a list of U.S. cities, HERE for Canadian cities and HERE for the rest of the world. Be aware that the times for Memphis and Minneapolis in the U.S. list are incorrectly shown as Eastern. Subtract an hour for the correct one. Here’s another interactive time link.